This invention relates to asbestos. More in particular, the present invention relates to a method of treating asbestos.
"Asbestos" is a general term applied to a group of naturally occurring fibrous silicate minerals that are commercially important because of their fibrous characteristics. Four principal types of asbestos minerals generally enter world commerce. These are chrysotile, crocidolite, amosite and anthophyllite. Of these, chrysotile is perhaps the most important, accounting for about 95 percent of the world's asbestos production.
Chemically, chrysotile asbestos is the fibrous form of the mineral serpentine, a hydrated magnesium silicate having the general formula Mg.sub.3 Si.sub.2 O.sub.3 (OH).sub.4. Structurally the chrysotile asbestos is believed to consist of rolled up sheets formed from two layers. The first layer is a continuous network of silica (SiO.sub.2) tetrahedra. This layer is interlocked through common oxygen atoms with a second layer of magnesium hydroxide (Mg(OH.sub.2)) octahedra. The walls of the asbestos fibers are composed of a number of such individual sheets contorted into scrolls with the magnesium hydroxide layer on the outside. Consequently, one of the dominant chemical features of chrysotile asbestos is its alkaline surface characteristics.
The surface modification of asbestine minerals, such as chrysotile, has attracted a good deal of attention from research workers during recent years. A large number of surface treatment methods have been proposed and evaluated for the purpose of modifying certain predetermined properties of the asbestos fibers. These procedures include: coating the surface of asbestos fibers with a phosphate, polyphosphate, or corresponding acid to improve the filtration characteristic of the fibers (U.S. Pat. Nos. 3,535,150, 3,957,571); treating asbestos fibers with magnesium carbonate or an oxide of a polyvalent metal to enhance the tensile strength of the fibers (U.S. Pat. Nos. 1,982,542; 2,451,805; 2,460,734); coating an asbestos fabric with an insoluble inorganic oxide to render the fabric flame resistant and water repellent (U.S. Pat. No. 2,406,779); mixing a detergent organic surface-active agent with fibrous asbestos agglomerates to disperse the asbestos fibers (U.S. Pat. No. 2,626,213); and distributing small amounts of polymeric particles or a water-soluble macromolecular organic substance throughout an asbestos product to reduce dust emitted by the asbestos during handling and use (U.S. Pat. Nos. 3,660,148; 3,967,043).
An area of concern to the producers and users of asbestine material has been the potential health problems allegedly associated with asbestos exposure. It has been reported by the National Safety Council that persons who inhale large amounts of asbestos dust can develop disabling or fatal pulmonary and pleural fibrosis (asbestosis) and several types of malignancy of the respiratory tract ("Asbestos," National Safety Council Newsletter, R & D Section, June 1974). There is also speculation that asbestos may cause various forms of carcinogenesis, particularly carcinoma of the lung, pleura and peritoneum (R. F. Holt, "Asbestosis," Nature, 253, 85 (1975)). Since the pathogenicity of asbestos minerals is apparently unmatched by any other silicate, there has been much interest in developing a method of passivating asbestos to reduce any potential fibrogenic and carcinogenic effects on those exposed to it without adequate precaution.
Existing methodology for studying the in vivo fibrogenic effects of asbestos involves direct inhalation or intratracheal administration of asbestos fibers to animals. Subsequently, the experimentally treated animals are examined, usually months later, for pathological and histochemical evidence of fibrosis. Since the incubation period for asbestos-induced diseases is reported to be unusually long, experiments of this type are complicated, expensive and time consuming.
However, recent work done by R. R. Hefner, Jr. and P. J. Gehring (American Industrial Hygiene Association Journal, 36, 734-740 (1975)) shows that a relationship exists between the in vivo fibrogenicity of asbestos and its in vitro hemolytic activity. Hemolytic activity, or hemolysis, is a measure of induced blood cell rupture when fibers are agitated with a suspension of blood erythrocytes. Numerous other authors have also made similar in vitro evaluations of a number of particulates.
The in vitro hemolytic model provides a rapid, relatively inexpensive test which reliably assesses the fibrogenic potential of asbestos. Consequently, the hemolytic model has been employed in the present invention to test the effectiveness of certain asbestos treating procedures found to be potentially useful in alleviating some of the health problems reportedly associated with asbestos fibers.
Various materials have been examined which interact with the surface of asbestos fibers and reduce its hemolytic activity. Such material includes disodium ethylenediamine tetraacetic acid (EDTA), simple phosphates, disodium versenate, polyvinylpyridine N-oxide and aluminum (G. Macnab and J. S. Harington, Nature 214, 522-3 (1967), and certain acidic polymers (R. J. Schnitzer and F. L. Pundsack, Environmental Research 3, 1-14 (1970). In addition, West German Pat. No. 1,642,022 discloses that asbestos coated with polyvinylpyridine N-oxide minimizes the risk of asbestosis.
Some of these known materials, such as EDTA, are solubilized in body fluids and do not reduce the long term hemolytic activity of the asbestos. There is therefore a need to determine materials which will adhere to the asbestos and reduce its hemolytic activity. Such passivating materials should not adversely affect the useful commercial properties of the asbestos.